This invention relates to offshore drilling rigs and more particularly, to structures in a rig for storing riser pipe sections and blowout preventors in a vertical condition below the derrick floor and for transporting such units in vertical condition between storage and operational areas.
In offshore drilling rigs, it is customary to have a string of interconnected tubular pipe sections extending from the rig to a blowout preventor means (sometimes hereinafter referred to as BOP) set on the ocean floor. The drilling string is then inserted through the tubular pipe string (called a "riser") for the drilling of the earth formations below the ocean floor.
On most rigs during the installation or removal of a riser pipe system, the riser is set or supported dependently on the rotary table and connections of riser pipe sections are made at the rig or derrick floor level. When not in use, the lengths of riser pipe sections are usually passed through a V-door and supported horizontally on a pipe rack by means of a rig crane. This manipulation of a riser pipe sections between a horizontal position on a pipe rack and a vertical passage through the rotary table is similar to the operation required for running casing strings. The operation requires virtually the full drilling crew as well as crane operators and roustabouts.
During rough weather, the riser sections are hard to control while hanging on the crane-sling lines. Tag lines are an aid but the chance for injury to personnel or damage to the riser is great. Actually, the problem of retrieving riser sections often comes about because of bad weather where it is desired to pull the riser string.
In the present invention, enough clearance is provided between a lower cellar deck and the derrick floor to rack or store the riser sections vertically under the derrick floor. The advantages of this concept include:
1. The need to lay down the riser pipe joints on the pipe rack is eliminated; PA1 2. Wind or dynamic loading on the derrick is not increased as it would be if the riser were racked in the derrick; PA1 3. More pipe rack area is available for other tubulars; PA1 4. The hazard to equipment and personnel created by frequent crane handling is eliminated; PA1 5. The same storage area is used for transit that is used while pulling or running; PA1 6. The number or personnel required to handle the riser is reduced; PA1 7. The time necessary to run or pull the riser is decreased; and PA1 8. The capability for handling the riser in more severe weather is increased.